If I recall correctly, the shell of the car is what is left at the Daytona USA museum for the year, not the engine, which is the most critical component of the vehicles and the most expensive and time consuming piece of equipment. Most teams, at least the bigger teams have a few shells ready to go at all times and plug and play the engines between them depending on the track and the condition of the shell. So it isn't a huge disadvantage unless you are racing for a team that only has 1 or 2 shells in reserve, in which case I'm sure NASCAR would grant an exception to the team to pull their shell.